The global efforts on preserving the health of the planet are focused in some key area like global warming and environmental air quality. One aspect of improving environmental air quality relates to technologies where the gases (e.g., carbon dioxide) that are released from manufacturing processes are captured and sequestered.
Capturing and sequestering gases may in the near future involve tightly controlled processes that include continuous real-time monitoring of emissions. The processes and monitoring that are typically associated with capturing and sequestering gases often require high cost-high power sensors.
One potential technology that may be utilized to produce low-cost and low-power sensors involves integrated resonant sensing technology. This integrated sensing technology is based on vibrating beams that are functionalized for chemisorptive carbon dioxide capture. The beams are typically doubly clamp (nano)beams, cantilever (nano)beams or even nanowires. The beams change their resonance frequency proportional to the amount of gas adsorbed on the beam.
These functionalized resonant sensing beams are typically located on the same chip with an integrated circuit for processing signals from the carbon dioxide sensor. A typical single silicon wafer having diameter of 400 mm may contain hundreds of thousands of on-chip carbon dioxide Nano-Electro-Mechano Sensors and Integrated Circuits (NEMSIC) that communicate with the readout integrated circuit.
One of the drawbacks with existing resonant NEMSIC gas sensing systems may relates to an inability to mass produce such systems. One of the difficulties that is associated with mass producing such systems is the low thermal tolerance of the functionalized resonating beams that are typically a primary component in these types of sensors. The low thermal tolerance is due to the fact that the functionalized resonating beams are usually made of organic materials whose chemical stability deteriorates at temperatures higher than 60-70° C. Since many manufacturing methods require temperate above 60-70° C., it becomes difficult to mass produce sensors that include functionalized resonating beams.
There is a need for a method of fabricating sensors that include functionalized resonating beams which allows (i) preparation of sensing layers in functionalized resonating beams; (ii) cost effective high volume packaging of the sensors, (iii) compatibility with the thermal limits tolerated by the organic material that is used in functionalized resonating beams; and (iv) the sensing surface to have access to the ambient air in order detect a reversible reaction between a particular gas in the ambient air and the functionalized resonating beams.